Biotic Regulation: Your questions

Question No. 30

In “Ecology and life” magazine (No. 10, 2010, in Russian) there was an article “Global ecological crisis and biotic regulation” by V. Savenko. The author considers evidence from geochemistry, the so-called “big” or geological matter cycling, which is not affected by the regulatory functioning of the biota. In other words, some limits to the biotic regulation theory are outlined. I would be grateful for your comments on this matter. Thanks in advance.

Atmospheric carbon dioxide is crucially important for the biota. The biotic regulation concept predicts that if there is an abiotic physicochemical process changing atmospheric concentration of carbon dioxide, the biota must arrange a compensatory process in such a manner that the dangerous deviations of atmospheric carbon amounts from the biotic optimum are ruled out.

The available data on the geophysical, geochemical and biotic fluxes of carbon as well as the observed constancy of atmospheric carbon content over on a geological time scale confirms the above prediction.

Specifically:

1. There is an inflow of inorganic carbon (CO2) into the atmosphere from the Earth's interior, in particular, in the course of volcanic activity. This process is not controlled the biota.

2. The rate of this inflow coincides, in its order of magnitude, with the rate at which carbon of biogenic origin is deposited in sediments.

3. This means that there is a compensatory reaction of the biota on the abiotic disturbance of atmospheric carbon content by geophysical processes.

4. In the result, despite significant disturbance, atmospheric concentration of carbon dioxide remains relatively constant preserving its order of magnitude for several hundred million years.

Savenko (2010) points out that a certain part of the deposited organic carbon can undergo chemical transformations in the Earth's interior and return to the atmosphere as carbon dioxide. Savenko (2010) emphasizes, that this process, which occurs outside the biosphere, cannot be controlled by the biota -- thus essentially agreeing with point 1 above.

However, from this Savenko (2001), as well as some other researchers cited by him, concludes, that the existence of life is only possible in the presence of such an abiotic inflow. The proposed reason is that only such an abiotic inflow can compensate the outflow of carbon from the atmosphere. This conclusion is incorrect, because the carbon outflow from the biosphere (not only in its organic form but also in the form of biogenic inorganic carbon synthesized by the biota in the form of shells and other inorganic constituents of living organisms) is itself under biotic control. This outflow only exists in its observed magnitude because the biota must get rid of the excessive carbon continuously arriving to the atmosphere from the Earth's interior. If this geophysical carbon inflow into the atmosphere were non-existent or negligible, so would be the biotically controlled carbon outflow from the atmosphere. The biota would be organized in a different way.

White Sea mollusc

Savenko (2010) also states that formation of carbonates that remove carbon dioxide during silicate weathering occurs at such a high rate that it could totally deplete the atmospheric carbon pool on a time scale of the order of 300 hundred years or less, and that there is no reverse compensatory biotic process. This would mean that life is under the mercy of the geophysical processes. However, this conclusion is also incorrect. The oceanic biotic pump (not to be confused with the biotic pump of atmospheric moisture) determines the vertical profile of carbon dioxide concentration, which rises from the oceanic surface towards the oceanic bottom. By changing the vertical profile of decomposition of organic matter within the oceanic ecological community the biota can substantially change the profile of carbon dioxide concentration thus shifting the equilibrium between CO2, carbonates and bicarbonates towards formation or depletion of CO2. As noted above, biotia also directly controls the rate at which carbonates are synthesized by the living organisms. On land weathering is also profoundly impacted by the biota, which, according to recent evidence, controls among other things the magnitude of river runoff.

Finally, the article averts from addressing the main point (see point 4 above): the observed constancy of atmospheric carbon content on a time scale of a billion years. It is emphasized in the biotic regulation concept that this constancy cannot be explained without involving biotic control. The difference between the rates of abiotic fluxes of inflow and outflow of atmospheric carbon is of the same order of magnitude as each of these fluxes (see Gorshkov 1995 "Physical and biological bases of life stability", p. 5). Physically different abiotic processes that add or remove carbon to/from the atmosphere, each being able to change the atmospheric carbon content by an order of magnitude on a geologically instantaneous time scale, could not have been compensating each other for a billion years by mere chance.